1 3/4-1 7/8 stepped vs. 1 7/8
10-28-2010, 08:34 PM
#43
Nothing to add other then I went through this when I ordered headers. At the time the general consences was the 17/8 was too large for a stock cube motor. Thinking that I would eventually want to go to a bigger cube motor but didn't want to loose torque with the 347 I choose stepped.
10-30-2010, 07:45 PM
#45
Well, when I was building headers for my 1989 Trans Am I did a lot of research and talked to quite a few people in the business. As said above the idea is to keep the exhaust velocity up and this will improve the scavenging process especially during the cam overlap period. This probably what the 1 3/4" headers do.
I also learned that around the first 8" of the header is the key velocity wise. Now say after the first 8" stepping up to 1 7/8" the rest of the way will help reduce any back pressure and if the step is done properly will also help in reducing reversion. Every time there is a bend in the tubing there is a loss of flow. A larger tube will help in reducing that flow loss.
However in order to fit the long tube headers in our cars bends are a necessary evil. The bigger the radius the better but again to fit the headers in the car we have to use a radius that allows the headers to fit in the space allowed.
By the way when I engine dyno tested my motor I compared my home-built 1 3/4" "shorty" headers to the dyno rooms long tube headers. There are reasons I have to use shorties so don't even ask. Hahaha. The results were below peak torque the long tube headers were better. Above peak torque and we are talking 5000rpm to 6500 rpm the dyno room headers were better by just 1+hp on average.
I also learned that around the first 8" of the header is the key velocity wise. Now say after the first 8" stepping up to 1 7/8" the rest of the way will help reduce any back pressure and if the step is done properly will also help in reducing reversion. Every time there is a bend in the tubing there is a loss of flow. A larger tube will help in reducing that flow loss.
However in order to fit the long tube headers in our cars bends are a necessary evil. The bigger the radius the better but again to fit the headers in the car we have to use a radius that allows the headers to fit in the space allowed.
By the way when I engine dyno tested my motor I compared my home-built 1 3/4" "shorty" headers to the dyno rooms long tube headers. There are reasons I have to use shorties so don't even ask. Hahaha. The results were below peak torque the long tube headers were better. Above peak torque and we are talking 5000rpm to 6500 rpm the dyno room headers were better by just 1+hp on average.
Last edited by 1989GTA; 10-30-2010 at 07:52 PM.
10-31-2010, 12:17 AM
#46
wow, that is very interesting. so i guess, and correct me if im wrong, from what the above poster is saying is confirming what i thought to begin with. That you still get the torque with the 1 3/4 primaries and get the peak power with the 1 7/8 stepped, which would be best for a stock cube ls1 or 6.0.
I would love to see some dyno graphs of some comparisons: hint hint to some sponsors
I would love to see some dyno graphs of some comparisons: hint hint to some sponsors
